Tending Nature's Garden

Abstract

S unrise in a tropical forest is never quiet. Monkeys bicker over breakfast. Birds clamor for the attention of mates. Insects chirp and twang as they go about their morning business. If plants made noises, they would contribute to the din. Instead, inaudibly, neighboring trees bicker about sharing sunlight. Colorful canopy blossoms clamor for the attention of pollinators. Roots tussle over water. A sapling groans because a fungal infection is girdling its trunk. For almost 3 centuries, biologists from temperate lands have tried to tune in to these silent tiffs. Often, the diversity of the tropics has stymied them. The forests these biologists are familiar with have a tenth as many species per acre, and winter's cold tends to silence the flora for months at a time. [Coming to the tropics] completely shatters everything you thought you knew and everything you thought was true, says Catherine Potvin, an ecologist at McGill University in Montreal. We have acquired knowledge about how northern systems work, and yet we have no clue as to what's going on here [in the tropics]. It's much more difficult, much more complex, much more stochastic. For years, these travelers have appreciated all too well the diversity and dynamic nature of these green paradises. But they have been unable to glean why or how these conditions come about. Yet just as zoologists have managed to attach meaning to animal chatter and from that figure out predictable patterns of behavior, botanists and ecologists have started to distinguish patterns of tropical plant behavior. What biologists are looking for are ways competition is ameliorated so all these species can coexist, explains S. Joseph Wright, a tropical ecologist at the Smithsonian Tropical Research Institute (STRI) in Balboa, Panama. Do plants jostle each other to get and keep a place in the sun? Or do they let animals or other organisms control their fates? Wright and others find that seemingly random events weather, predators, pathogens can dictate which trees sprout or survive at any given time. They also help ensure that no one species outcompetes all the rest. Because each plant differs in how it harnesses the available resources be they water, light, pollinators, even seed dispersers each does better or worse in certain conditions. Researchers have begun to sense that these differences lead to complex patterns. As conditions change, so does an individual species' fitness. Over time, one type of tree may give way to another, and the mix of species that is, the community structure shifts.